Manufacturing systems often require surface inspection to detect flaws and contamination that render a product unsuitable for sale. For example, surface inspection systems are utilized to inspect moving webs of materials. A “web” is a flat material produced continuously in large quantities and at very high rates. Typical web material includes fabrics, sheet metal, paper, and non-woven plastic, etc. Inspection of the web material surface is required during production to find flaws and defects. Failure to detect these flaws and defects may result in thousands of feet of unusable web material.
Automated inspection systems of surfaces for defects typically utilize cameras which capture images of the surface under inspection. The images are then evaluated using hardware and/or software to detect defects. Proper illumination of the surface under inspection is essential for acceptable imaging by the cameras. A basic illumination system consists of a bright light source that is distributes uniform light across the surface under inspection. However, this basic illumination results in “flat” or two-dimensional images which may not reveal the presence of defects on the surface. Flat images often highlight dust on the inspected surface resulting in false identification of defects.
The use of multiple light sources which are directed at the surface enhances the visual appearance of materials that are under inspection. For example, multiple light sources may be positioned to illuminate the surface from various angles. The light sources may utilized varying wavelengths of light to enhance surface features. Some systems strobe or sequentially switch lights to enhance camera images. Defects which cannot be seen with uniform illumination become visible when utilizing these types of illumination schemes.
The above-described illumination systems present disadvantages of use in a surface inspection system. Flat illumination does not provide sufficient lighting for a camera to detect small defects. Because flat illumination highlights dust on the surface, this type of illumination may not be suitable for harsh environments. The use of multiple light sources increases the cost of a defect detection system as well as the cost for operation of the system. Strobe or switched lights require switching and control hardware which increases cost and complexity of the system. In addition, the existing illumination systems limit the resolution of the defect detection. Therefore, a need continues to exist for an illumination source for use in a defect detection system that allows a camera to produce images of easily-identifiable defects.